DNS Security (DNSSEC) Experiments
RFC 4955

Network Working Group                                          D. Blacka
Request for Comments: 4955                                VeriSign, Inc.
Category: Standards Track                                      July 2007

                   DNS Security (DNSSEC) Experiments

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes a methodology for deploying alternate, non-
   backwards-compatible, DNS Security (DNSSEC) methodologies in an
   experimental fashion without disrupting the deployment of standard
   DNSSEC.

Table of Contents

   1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Definitions and Terminology . . . . . . . . . . . . . . . . . . 2
   3.  Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   4.  Method  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   5.  Defining an Experiment  . . . . . . . . . . . . . . . . . . . . 4
   6.  Considerations  . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Use in Non-Experiments  . . . . . . . . . . . . . . . . . . . . 5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

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1.  Overview

   Historically, experimentation with DNSSEC alternatives has been a
   problematic endeavor.  There has typically been a desire to both
   introduce non-backwards-compatible changes to DNSSEC and to try these
   changes on real zones in the public DNS.  This creates a problem when
   the change to DNSSEC would make all or part of the zone using those
   changes appear bogus (bad) or otherwise broken to existing security-
   aware resolvers.

   This document describes a standard methodology for setting up DNSSEC
   experiments.  This methodology addresses the issue of coexistence
   with standard DNSSEC and DNS by using unknown algorithm identifiers
   to hide the experimental DNSSEC protocol modifications from standard
   security-aware resolvers.

2.  Definitions and Terminology

   Throughout this document, familiarity with the DNS system (RFC 1035
   [5]) and the DNS security extensions (RFC 4033 [2], RFC 4034 [3], and
   RFC 4035 [4]) is assumed.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

3.  Experiments

   When discussing DNSSEC experiments, it is necessary to classify these
   experiments into two broad categories:

   Backwards-Compatible:  describes experimental changes that, while not
      strictly adhering to the DNSSEC standard, are nonetheless
      interoperable with clients and servers that do implement the
      DNSSEC standard.

   Non-Backwards-Compatible:  describes experiments that would cause a
      standard security-aware resolver to (incorrectly) determine that
      all or part of a zone is bogus, or to otherwise not interoperate
      with standard DNSSEC clients and servers.

   Not included in these terms are experiments with the core DNS
   protocol itself.

   The methodology described in this document is not necessary for
   backwards-compatible experiments, although it certainly may be used
   if desired.

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4.  Method

   The core of the methodology is the use of strictly unknown algorithm
   identifiers when signing the experimental zone, and more importantly,
   having only unknown algorithm identifiers in the DS records for the
   delegation to the zone at the parent.

   This technique works because of the way DNSSEC-compliant validators
   are expected to work in the presence of a DS set with only unknown
   algorithm identifiers.  From RFC 4035 [4], Section 5.2:

      If the validator does not support any of the algorithms listed in
      an authenticated DS RRset, then the resolver has no supported
      authentication path leading from the parent to the child.  The
      resolver should treat this case as it would the case of an
      authenticated NSEC RRset proving that no DS RRset exists, as
      described above.

   And further:

      If the resolver does not support any of the algorithms listed in
      an authenticated DS RRset, then the resolver will not be able to
      verify the authentication path to the child zone.  In this case,
      the resolver SHOULD treat the child zone as if it were unsigned.

   Although this behavior isn't strictly mandatory (as marked by MUST),
   it is unlikely for a validator to implement a substantially different
   behavior.  Essentially, if the validator does not have a usable chain
   of trust to a child zone, then it can only do one of two things:
   treat responses from the zone as insecure (the recommended behavior),
   or treat the responses as bogus.  If the validator chooses the
   latter, this will both violate the expectation of the zone owner and
   defeat the purpose of the above rule.  However, with local policy, it
   is within the right of a validator to refuse to trust certain zones
   based on any criteria, including the use of unknown signing
   algorithms.

   Because we are talking about experiments, it is RECOMMENDED that
   private algorithm numbers be used (see RFC 4034 [3], Appendix A.1.1.
   Note that secure handling of private algorithms requires special
   handing by the validator logic.  See "Clarifications and
   Implementation Notes for DNSSECbis" [6] for further details.)
   Normally, instead of actually inventing new signing algorithms, the
   recommended path is to create alternate algorithm identifiers that
   are aliases for the existing, known algorithms.  While, strictly
   speaking, it is only necessary to create an alternate identifier for
   the mandatory algorithms, it is suggested that all optional defined
   algorithms be aliased as well.

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   It is RECOMMENDED that for a particular DNSSEC experiment, a
   particular domain name base is chosen for all new algorithms, then
   the algorithm number (or name) is prepended to it.  For example, for
   experiment A, the base name of "dnssec-experiment-a.example.com" is
   chosen.  Then, aliases for algorithms 3 (DSA) and 5 (RSASHA1) are
   defined to be "3.dnssec-experiment-a.example.com" and
   "5.dnssec-experiment-a.example.com".  However, any unique identifier
   will suffice.

   Using this method, resolvers (or, more specifically, DNSSEC
   validators) essentially indicate their ability to understand the
   DNSSEC experiment's semantics by understanding what the new algorithm
   identifiers signify.

   This method creates two classes of security-aware servers and
   resolvers: servers and resolvers that are aware of the experiment
   (and thus recognize the experiment's algorithm identifiers and
   experimental semantics), and servers and resolvers that are unaware
   of the experiment.

   This method also precludes any zone from being both in an experiment
   and in a classic DNSSEC island of security.  That is, a zone is
   either in an experiment and only possible to validate experimentally,
   or it is not.

5.  Defining an Experiment

   The DNSSEC experiment MUST define the particular set of (previously
   unknown) algorithm identifiers that identify the experiment and
   define what each unknown algorithm identifier means.  Typically,
   unless the experiment is actually experimenting with a new DNSSEC
   algorithm, this will be a mapping of private algorithm identifiers to
   existing, known algorithms.

   Normally the experiment will choose a DNS name as the algorithm
   identifier base.  This DNS name SHOULD be under the control of the
   authors of the experiment.  Then the experiment will define a mapping
   between known mandatory and optional algorithms into this private
   algorithm identifier space.  Alternately, the experiment MAY use the
   Object Identifier (OID) private algorithm space instead (using
   algorithm number 254), or MAY choose non-private algorithm numbers,
   although this would require an IANA allocation.

   For example, an experiment might specify in its description the DNS
   name "dnssec-experiment-a.example.com" as the base name, and declare
   that "3.dnssec-experiment-a.example.com" is an alias of DNSSEC
   algorithm 3 (DSA), and that "5.dnssec-experiment-a.example.com" is an
   alias of DNSSEC algorithm 5 (RSASHA1).

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   Resolvers MUST only recognize the experiment's semantics when present
   in a zone signed by one or more of these algorithm identifiers.  This
   is necessary to isolate the semantics of one experiment from any
   others that the resolver might understand.

   In general, resolvers involved in the experiment are expected to
   understand both standard DNSSEC and the defined experimental DNSSEC
   protocol, although this isn't required.

6.  Considerations

   There are a number of considerations with using this methodology.

   1.  If an unaware validator does not correctly follow the rules laid
       out in RFC 4035 (e.g., the validator interprets a DNSSEC record
       prior to validating it), or if the experiment is broader in scope
       that just modifying the DNSSEC semantics, the experiment may not
       be sufficiently masked by this technique.  This may cause
       unintended resolution failures.

   2.  It will not be possible for security-aware resolvers unaware of
       the experiment to build a chain of trust through an experimental
       zone.

7.  Use in Non-Experiments

   This general methodology MAY be used for non-backwards compatible
   DNSSEC protocol changes that start out as or become standards.  In
   this case:

   o  The protocol change SHOULD use public IANA allocated algorithm
      identifiers instead of private algorithm identifiers.  This will
      help identify the protocol change as a standard, rather than an
      experiment.

   o  Resolvers MAY recognize the protocol change in zones not signed
      (or not solely signed) using the new algorithm identifiers.

8.  Security Considerations

   Zones using this methodology will be considered insecure by all
   resolvers except those aware of the experiment.  It is not generally
   possible to create a secure delegation from an experimental zone that
   will be followed by resolvers unaware of the experiment.

   Implementers should take into account any security issues that may
   result from environments being configured to trust both experimental
   and non-experimental zones.  If the experimental zone is more

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   vulnerable to attacks, it could, for example, be used to promote
   trust in zones not part of the experiment, possibly under the control
   of an attacker.

9.  References

9.1.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
        "DNS Security Introduction and Requirements", RFC 4033,
        March 2005.

   [3]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
        "Resource Records for the DNS Security Extensions", RFC 4034,
        March 2005.

   [4]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
        "Protocol Modifications for the DNS Security Extensions",
        RFC 4035, March 2005.

9.2.  Informative References

   [5]  Mockapetris, P., "Domain names - implementation and
        specification", STD 13, RFC 1035, November 1987.

   [6]  Weiler, S. and R. Austein, "Clarifications and Implementation
        Notes for DNSSECbis", Work in Progress, March 2007.

Author's Address

   David Blacka
   VeriSign, Inc.
   21355 Ridgetop Circle
   Dulles, VA  20166
   US

   Phone: +1 703 948 3200
   EMail: davidb@verisign.com
   URI:   http://www.verisignlabs.com

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   Copyright (C) The IETF Trust (2007).

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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